This section provides background information related to the present disclosure which is not necessarily prior art.
The current mobile IM technology has been developed by combining the mobile communication technology and the IM technology. With the mobile IM technology, a mobile subscriber can log in an IM system through a mobile communication system and deliver an instant message or a file such as a picture, a voice file, a video file and a text with another mobile subscriber having logged in the IM system, thereby implementing various instant messaging services between mobile subscribers. At present, however, the delivery of an instant message or a file such as a picture, a voice file, a video file and a text between mobile subscribers has to be implemented on the premise that both of the mobile subscriber as a sender and the mobile subscriber as a receiver, respectively have logged in the IM system, i.e. they are in an on line state with respect to the IM system at the same time, which greatly limits the application of the mobile IM technology to the mobile communication system.